This invention relates to a discharge lamp lighting device with a power source of an commercial AC and an illumination device equipped with the discharge lamp lighting device, and more particularly to those capable of lighting the discharge lamp with high power factor.
Referring to FIG. 9, an explanation will be given of a conventional discharge lamp device. FIG. 9 is a circuit diagram of a conventional discharge lamp device which is disclosed in e.g. JP-A-9-45490.
In FIG. 9, reference numeral 101 denotes a commercial power source; 102 a rectifying circuit; 103 a voltage boosting inverter; 104 a voltage dropping inverter; 105 a square wave circuit; 106 a starting circuit; 107 a discharge lamp; 108 a voltage-boosting inverter control circuit; 109 a voltage-dropping inverter control circuit; 110 a square wave control circuit; and 111 a control power source circuit.
Referring to the drawing, an explanation will be given of the operation of the conventional discharge lamp device. When electric power is supplied from a commercial A.C. power source 101, the control power source circuit 111 creates control power which is fed to the voltage-boosting inverter circuit 108, voltage dropping circuit 109 and square-wave control circuit 110. As a result, these circuits start to operate.
First, the AC power from the commercial AC power source 101 is rectified by the rectifying circuit 102, and the rectified power is applied to the voltage boosting inverter 103. The voltage-boosting inverter 103 converts the applied DC voltage into a DC voltage of 400 V. Then, the voltage boosting inverter control circuit 108 corrects wave distortion of an input current supplied to the voltage-boosting inverter 103 to control the voltage-boosting inverter 103 so that the input power factor is approximately 100%.
Next, the voltage-dropping inverter 104 inverts the DC voltage supplied from the voltage-boosting inverter 103 into a DC voltage corresponding to a load change in the discharge lamp 107. Then, the voltage-dropping-inverter control circuit 109 controls the output voltage from the voltage dropping inverter 104 so that the current flowing through the discharge lamp 107 is a prescribed current, e.g. a constant current of 2 A.
The square wave circuit 105 converts the DC voltage applied from the voltage dropping inverter 104 into an AC square wave. Then, the square wave control circuit 110 controls the square wave circuit 105 so that the current flowing through the discharge lamp 107 is an AC square wave at a prescribed frequency of e.g. 100 Hz.
The starting circuit 106 generates a high voltage pulse by the AC square wave from the square wave circuit 105 to start the lighting of the discharge lamp 107.
The discharge lamp device which has a low power factor exerts anadverse effect on a commercial AC power system facility so that the discharge lamp device with a high power factor has been demanded. In order to give the high power factor to the device, as in the conventional discharge lamp device, using the voltage boosting inverter 103, the AC voltage must be converted into a DC voltage.
However, where the discharge lamp device is equipped with the voltage-boosting inverter 103, since the voltage-boosting inverter 103 itself is bulky, heavy and expensive, the discharge lamp device also becomes bulky, heavy and expensive.
This invention has been accomplished in order to solve the problem described above, and intends to provide a discharge lamp lighting device and illumination device which can be miniaturized with a high power factor and also is inexpensive.
The discharge lamp lighting device according to this invention is characterized by comprising:
a rectifying circuit for full-wave rectifying a commercial AC power source;
a voltage boosting/dropping circuit for boosting or dropping a voltage from the rectifying circuit;
a control section for controlling the boosted/dropped voltage from the voltage boosting/dropping circuit;
a polarity changing circuit for changing the polarity of the current boosted or dropped by the voltage boosting/dropping circuit;
a discharge lamp through which the current from the polarity changing circuit is passed; and
a detecting section for detecting the zero crossing of the commercial AC power source, and in that
in response to a zero-crossing detected signal detected by the detecting section, the control section controls the voltage boosting/dropping circuit so that the current flowing through the discharge lamp is larger in the vicinity of the phases of 90xc2x0 and 270xc2x0 of the commercial AC power source than in the vicinity of the phases of 0xc2x0 and 180xc2x0 thereof.
The discharge lamp lighting device according to this invention is also characterized in that when the polarity of the current passed through the discharge lamp by the polarity changing circuit is changed at a frequency equal to or higher than that of the commercial AC power source, it is changed at least in the vicinity of the phases of 0xc2x0 and 180xc2x0 thereof.
The discharge lamp lighting device according to this invention is also characterized in that when the polarity of the current passed through the discharge lamp by the polarity changing circuit is changed at a frequency equal to or higher than that of the commercial AC power source, it is changed at least in the vicinity of the phases of 90xc2x0 and 270xc2x0 thereof.
The discharge lamp lighting device according to this invention is also characterized in that the detecting section has a function of detecting the phase of the commercial AC power source, and the control section controls the voltage boosting/dropping circuit and the polarity changing circuit changes the polarity of the flowing current so that the current flowing through the discharge lamp is substantially in phase with that of the commercial AC power source voltage and has a substantially sine waveform.
The discharge lamp lighting device according to this invention is also characterized in that the current flowing through the discharge lamp is constant in the vicinity of the phases of 90xc2x0 and 270xc2x0.
The discharge lamp lighting device according to this invention is also characterized in that the current flowing through the discharge lamp is the square of the sine wave in synchronism with the commercial AC power source voltage.
The discharge lamp lighting device according to this invention is also characterized by further comprising a voltage detecting section for detecting the voltage across the discharge lamp, and in that in response to the detected value from the voltage detecting section, the control section controls the voltage boosting/dropping circuit so that electric power supplied to the discharge lamp is constant.
The illumination device according to this invention is characterized by having a discharge lamp lighting device defined in any one of the discharge lamp lighting device described above.